Enrichment Mechanism of Phosphate in CaO-SiO2-FeO-Fe2O3-P2O5 Steelmaking Slags

The phosphate-enrichment behavior has experimentally been investigated in CaO-SiO₂-FeO-Fe₂O₃-P₂O₅ steelmaking slags. The reaction ability of structural units in the slags has been represented the mass action concentration \( N_{i} \) from the developed ion and molecule coexistence theory (IMCT)- \( N_{i} \) model based on the IMCT. The defined enrichment possibility \( N_{{{\text{c}}i{\text{ {-}c}}j}} \) and enrichment degree \( R_{{{\text{c}}i{\text{{-}c}}j}} \) of solid solutions containing P₂O₅ from the developed IMCT- \( N_{i} \) model have been verified from the experimental results. The effects of binary basicity, the mass percentage ratio \( {{ ( {\text{pct Fe}}_{t} {\text{O)}}} \mathord{\left/ {\vphantom {{ ( {\text{pct Fe}}_{t} {\text{O)}}} { ( {\text{pct CaO)}}}}} \right. \kern-0pt} { ( {\text{pct CaO)}}}} \) , and mass percentage of P₂O₅ in the initial slags on phosphate-enrichment behavior in the slags has also been discussed. The results show that the P₂O₅ component can easily be bonded by CaO to form tricalcium phosphate 3 CaO·P₂O₅, and the formed 3CaO·P₂O₅ can react with the produced dicalcium silicate 2CaO·SiO₂ to generate solid-solution 2CaO·SiO₂-3CaO·P₂O₅ under fixed cooling conditions. The maximum value of the defined enrichment degree \( R_{{{\text{C}}_{ 2} {\text{S{-}}} {\text{C}}_{ 3} {\text{P}}}} \) of solid-solution 2CaO·SiO₂-3CaO·P₂O₅ is obtained as 0.844 under conditions of binary basicity as 2.5 and the mass percentage ratio \( {{ ( {\text{pct Fe}}_{t} {\text{O)}}} \mathord{\left/ {\vphantom {{ ( {\text{pct Fe}}_{t} {\text{O)}}} { ( {\text{pct CaO)}}}}} \right. \kern-0pt} { ( {\text{pct CaO)}}}} \) as 0.955 at fixed cooling conditions.     

Prediction of the As-Cast Structure of Al-4.0 Wt Pct Cu Ingots

A two-stage simulation strategy is proposed to predict the as-cast structure. During the first stage, a 3-phase model is used to simulate the mold-filling process by considering the nucleation, the initial growth of globular equiaxed crystals and the transport of the crystals. The three considered phases are the melt, air and globular equiaxed crystals. In the second stage, a 5-phase mixed columnar-equiaxed solidification model is used to simulate the formation of the as-cast structure including the distinct columnar and equiaxed zones, columnar-to-equiaxed transition, grain size distribution, macrosegregation, etc. The five considered phases are the extradendritic melt, the solid dendrite, the interdendritic melt inside the equiaxed grains, the solid dendrite, and the interdendritic melt inside the columnar grains. The extra- and interdendritic melts are treated as separate phases. In order to validate the above strategy, laboratory ingots (Al-4.0 wt pct Cu) are poured and analyzed, and a good agreement with the numerical predictions is achieved. The origin of the equiaxed crystals by the “big-bang” theory is verified to play a key role in the formation of the as-cast structure, especially for the castings poured at a low pouring temperature. A single-stage approach that only uses the 5-phase mixed columnar-equiaxed solidification model and ignores the mold filling can predict satisfactory results for a casting poured at high temperature, but it delivers false results for the casting poured at low temperature.     

Microstructural Evolution of the Interdiffusion Zone between U-9 Wt Pct Mo Fuel Alloy and Zr-1 Wt Pct Nb Cladding Alloy Upon Annealing

Diffusion couple formed between U-9 wt pct Mo and Zr-1 wt pct Nb alloys, proposed as fuel and clad materials, respectively, in nuclear research reactors, was annealed to investigate the microstructural evolution of the interdiffusion zone (IZ) as a function of temperature. A layered-type IZ microstructure was observed, the mechanism of development of which was elucidated. Mo₂Zr phase, present as dispersoids, in the U-rich part of the as-bonded IZ evolved into a continuous layer and into a “massive” morphology upon annealing. The discontinuous precipitation reaction in the matrix adjoining the Mo₂Zr phase, instigated by Mo depletion, generated lamellae of α-U phase within the γ-U(Mo,Zr) matrix. Zr-rich α-Zr(U) precipitates were observed in U-rich U-Mo-Zr matrix in the IZ next to the U-9Mo base material due to the clustering tendency of the matrix phase. The IZ next to Zr-1Nb base material comprised a “basket weave” microstructure of α-Zr laths with β-Zr(Nb,U) interlath boundaries, wherein an omega like transformation of the latter to δ-UZr₂ was also noticed. The growth rates of the IZ were orders of magnitude lower when compared with the ones reported between the compositionally similar U-10 wt pct Mo alloy and the presently used Al or Al-Si cladding alloys.     

Solidification of Al-4.5 wt pct Cu-Replicated Foams

Microcellular Al-4.5 wt pct Cu of 400- or 75-μm average pore diameter is solidified at cooling rates ranging from ?30 K/min to ?0.45 K/min (?30 °C/min to ?0.45 °C/min). In the 400-μm pore size samples, the dendritic character is lost, and the level of microsegregation, which is quantified by the minimum copper content of the matrix, is reduced when the cooling rate is lowered. The 75-μm pore size samples show no dendritic microstructural features and low levels of microsegregation, even at the higher cooling rates explored. Microstructural maps, based on solidification theory developed for metal matrix composites, satisfactorily describe the microstructure of the Al-4.5 wt pct Cu foams. A finite difference model giving the minimum copper content as a function of the reinforcement size and cooling rate, developed for fiber-reinforced metals, is also valid for replicated Al-4.5 wt pct Cu foam. This work thus extends to particulate composites and, by extension, to replicated microcellular alloys, results originally derived from the study of fiber-reinforced metal solidification.     

A Study of the Viscous Properties with NaF Additions in the CaO-SiO<Subscript>2</Subscript>-12 mass pct Na<Subscript>2</Subscript>O Based Slags

The viscous behavior of the CaO-SiO₂-12 mass pct Na₂O based slag system with various concentrations of NaF has been studied using the rotating spindle method. NaF additions decreased the viscosity by interacting with bridged oxygens in the complex silicates and depolymerizing the network structure of the molten slag. NaF was particularly effective at lowering the viscosity in small amounts, but beyond 8 mass pct NaF, the effect was not as pronounced. A comparison between additions of NaF and CaF₂ revealed NaF to be more effective at decreasing the viscosity for 1523 K and 1573 K (1250 °C and 1300 °C). From the slopes of the Arrhenius relationship for viscosity, the activation energy of viscous flow was found to be between 128 kJ/mol to 115 kJ/mol, which were lower than the values for the same amount of CaF₂ additions. Both a temperature effect and a compositional effect on the molten slag structure and subsequently the viscous behavior were observed. The Fourier transformed infrared (FTIR) spectra taken for the CaO-SiO₂-12 mass pct Na₂O-8 mass pct NaF slag samples quenched from 1623 K to 1773 K (1350 °C to 1500 °C) revealed that the temperature effect on the viscosity was observed at temperatures below 1673 K (1400 °C).     

Warm Formability of 0.2 Pct C-1.5 Pct Si-5 Pct Mn Transformation-Induced Plasticity-Aided Steel

The warm stretch formability and flangeability of 0.2 pct C-1.5 pct Si-5 pct Mn transformation-induced plasticity-aided sheet steel with annealed martensite matrix were investigated for automotive applications. Both formabilities were enhanced by warm forming at peak temperatures of 423 K to 573 K and 423 K to 523 K (150 °C to 300 °C and 150 °C to 250 °C), respectively. The superior warm formabilities were mainly due to the stabilization of a large amount of retained austenite by warm forming and the consequent considerably suppressed void growth at the interface between the matrix and transformed martensite, despite there being large hole punching damage for the stretch flangeability. High peak temperatures for stretch formability and flangeability were associated with apparently increased M _S of the retained austenite resulting from the increased mean normal stress on stretch forming and hole expansion.     

Large Strain Deformation in Uranium 6 Wt Pct Niobium

The large strain deformation of polycrystalline uranium 6 wt pct niobium (U6Nb) was studied in situ during uniaxial tensile and compressive loading by time-of-flight neutron diffraction. Diffraction patterns were recorded at incremental strains to a maximum of approximately 0.13 tensile and 0.15 compressive true strain. A discrete reorientation of the crystallographic texture under tensile straining between 0.04 and 0.08 true strain is consistent with a previously unobserved mechanical deformation twinning mechanism, identified as either a (100) or (010) mechanical twin system. Beyond this, a continuous texture reorientation towards an (010) crystal orientations indicates that a slip mechanism is likely predominant. An analogous mechanical twin system was not observed in compression at large strain.     

Effect of TiO2 on Sintering and Grain Growth Kinetics of MgO from MgCl2·6H2O

The effect of TiO₂ on the grain growth kinetics of MgO prepared from MgCl₂·6H₂O was studied by the tradition phenomenological rate equation. The results showed that the addition of TiO₂ decreased the activation energy of MgO grain growth, accelerated the growth rate of MgO grain, and markedly promoted the sintering of MgO. Without TiO₂ addition, the MgO grain growth exponent $ n $ was 3, the grain growth activation energy $ Q $ was 556.9 kJ·mol^?1, and the process was considered as volume diffusion controlled. With 0.2 wt pct TiO₂ addition, the MgO grain growth exponent $ n $ was 2, the grain growth activation energy $ Q $ was 272.8 kJ·mol^?1, and the process was considered as interface diffusion controlled. The apparent and closed porosities of MgO-0.2 wt pct TiO₂ sample were decreased significantly, and the bulk density increased to 3.49 g·cm^?3 (relative density is 97.5 pct). The main mechanism of TiO₂ promoting the sintering of MgO was that TiO₂ solubilized in MgO to form unequivalence substitutional solid solutions and cation vacancies that were favorable to cation diffusion.     

Microstructure Evolution of Atomized Al-0.61 wt pct Fe and Al-1.90 wt pct Fe Alloys

The microstructure evolution of impulse atomized powders of Al-0.61 wt pct and Al-1.90 wt pct Fe compositions have been investigated with a scanning electron microscope, transmission electron microscope, neutron diffraction, and backscattering electron diffraction (EBSD). Both hypoeutectic and hypereutectic compositions demonstrated similar macrostructure (i.e., primary α-Al dendrites/cells with eutectic Al-Fe intermetallics decorated at the dendritic/cellular walls). Selected area electron diffraction (SAED) analysis and SAED pattern simulation identified the eutectic Al-Fe intermetallic as Al_mFe (m = 4.0-4.4). This is verified by neutron diffraction analysis. Cubic texture was observed by EBSD on the droplets with dendritic growth direction close to 〈111〉. The possible reasons are discussed.     

Rare earth doping effects on superconducting properties of MgB2: A review

Rare earth (RE) elements and their compounds have been doped into MgB₂ since the discovery of the superconductivity of MgB₂. The doping effects of RE elements and RE compounds are summarized in terms of different doping methods and the accompanying variations in the superconducting transition temperature, upper critical field, irreversibility field, and critical current density (J_c). Conclusions are drawn on the doping mechanisms to demonstrate the possibility of improvement of J_c in the future. REB_y phase inclusions are observed in MgB₂ as nano-pinning centers with significant enhancement of J_c in MgB₂ doped with Y, La, Dy, Ho, Nd, etc. Furthermore, some REs with larger magnetic moments will provide more efficient flux pinning centers with larger pinning forces, which is different with the doping effects and mechanism of ferromagnetic transition metals in MgB₂. The co-doping effects of RE with other dopants are also reviewed due to the multiple advantages of different doping mechanisms.     

Effect of Carbon on Microstructure and Mechanical Properties of Low C-1.6 pct Mn-0.1 pct Cr-0.3 pct Mo-0.0005 pct B Dual-Phase Steels

Effect of carbon on the microstructure and mechanical properties of 0.011 and 0.032 pct carbon dual-phase steels was investigated. r _m value was increased to 1.52 at around 400 MPa tensile strength level through the optimal design in the steel chemistry and proper control of phase transformation during continuous galvanizing cycle. The isolated martensite particles are expected to increase the strength but are expected not to be desirable for the deep drawability.     

Selective Oxidation and Reactive Wetting of 1.0 Pct Si-0.5 Pct Al and 1.5 Pct Si TRIP-Assisted Steels

Heat treatments were performed using an isothermal bainitic transformation (IBT) temperature compatible with continuous hot-dip galvanizing on two high Al–low Si transformation induced plasticity (TRIP)-assisted steels. Both steels had 0.2 wt pct C and 1.5 wt pct Mn; one had 1.5 wt pct Al and the other had 1 wt pct Al and 0.5 wt pct Si. Two different intercritical annealing (IA) temperatures were used, resulting in intercritical microstructures of 50 pct ferrite (α)-50 pct austenite (γ) and 65 pct α-35 pct γ. Using the IBT temperature of 465 °C, five IBT times were tested: 4, 30, 60, 90, and 120 seconds. Increasing the IBT time resulted in a decrease in the ultimate tensile strength (UTS) and an increase in the uniform elongation, yield strength, and yield point elongation. The uniform elongation was higher when using the 50 pct α-50 pct γ IA temperature when compared to the 65 pct α-35 pct γ IA temperature. The best combinations of strength and ductility and their corresponding heat treatments were as follows: a tensile strength of 895 MPa and uniform elongation of 0.26 for the 1.5 pct Al TRIP steel at the 50 pct γ IA temperature and 90-second IBT time; a tensile strength of 880 MPa and uniform elongation of 0.27 for the 1.5 pct Al TRIP steel at the 50 pct γ IA temperature and 120-second IBT time; and a tensile strength of 1009 MPa and uniform elongation of 0.22 for the 1 pct Al-0.5 pct Si TRIP steel at the 50 pct γ IA temperature and 120-second IBT time.     

Study on Microstructures of Al-4 wt pct V Master Alloys

Aluminum (Al)-V master alloys have attracted attention, because they can potentially be efficient grain refiners for wrought aluminum alloys. In this paper, the microstructure and factors affecting the microstructure of Al-4 wt pct V master alloys were investigated by means of controlled melting and casting processes followed by structure examination. The results showed that the type and morphology of the V-containing phases in Al-V master alloys were strongly affected by the temperature of the melt, concentration of vanadium in solution in the melt and the cooling conditions. Two main V-containing phases, Al₃V and Al₁₀V, which have different shapes, were found in the alloys prepared by rapid solidification. The Al₃V phase formed when there were both a high temperature (1273 K to 1673 K (1000 °C to 1400 °C)) and a relatively high vanadium content of 3 to 4 wt pct, while the Al₁₀V phase formed at a low temperature (<1373 K (1100 °C)) or a low vanadium content in the range of 1 to 3 wt pct. The results also showed that the type of V-containing phase that formed in the Al-4 wt pct V master alloy was determined by the instantaneous vanadium content.     

Grain Size Effects on Primary,Secondary, and Tertiary Twin Development in Mg-4 wt pct Li (-1 wt pct Al) Alloys

Grain size effects on three generations of twins were investigated in extruded Mg-4 wt pct Li (-1 wt pct Al) alloys using electron-backscatter diffraction. Samples with three distinct grains sizes, yet the same texture and applied strain were analyzed. With these variables fixed, we show that compression and double twinning decrease substantially with decreasing grain size. We find that compression twinning exhibits a stronger grain size effect than tension twinning, whereas the compression twinning to double twinning transition is independent of grain size.     

Microstructural Evolution of the 55 Wt Pct Al-Zn Coating During Press Hardening

Press hardening is increasingly being used to produce ultra-high strength steel parts for passenger cars. Al-Si, Zn, and Zn-alloy coatings have been used to provide corrosion protection to press hardening steel grades. The use of coatings has drawbacks such as coating delamination or liquid metal-induced embrittlement. In the present work, the microstructural evolution of Al-Zn coating during press hardening was studied. The 55 wt pct Al-Zn coating can in principle provide both Al barrier protection and Zn cathodic protection to press hardened steel. During the heat treatment associated with the press hardening, the 55 wt pct Al-Zn alloy coating is converted to an intermetallic surface layer of Fe₂Al₅ and a FeAl intermetallic diffusion layer. The Zn is separated from both intermetallic compounds and accumulates at grain boundaries and at the surface. This Zn separation process is beneficial in terms of providing cathodic protection to Al-Zn coated press hardening steel.     

Activity Coefficient of SiO2 in SiO2-Al2O3-CaO Slags with Low SiO2-Content at 1873 K (1600 °C)

The activity coefficient of SiO₂ in SiO₂-Al₂O₃-CaO slags with limited Al₂O₃ content was measured by equilibrating Fe-C-Si melt and slags at 1873 K (1600 °C). When the Al₂O₃ content was between 48 and 54 wt pct, the results show that $ \gamma_{{{\text{SiO}}_{ 2} }} $ rapidly decreases as the amount of SiO₂ in the slag decreases. The equilibrium amounts of Si and Al in a Fe melt in equilibrium with SiO₂-Al₂O₃-CaO slags were calculated based on the result of this study.     

Microstructure of a Creep-Resistant 10 Pct Chromium Steel Containing 250 ppm Boron

The microstructure of a trial martensitic chromium steel containing a high content of boron (250 ppm) was characterized in detail in the as-tempered and aged conditions. This steel has a similar composition and heat treatment as the TAF steel that still is unsurpassed in creep strength among all 9 to 12 pct chromium steels. Characterization was performed by using scanning electron microscopy, energy-filtered transmission electron microscopy, secondary ion mass spectroscopy, and atom probe tomography. Focus was placed on investigating different types of precipitates that play a key role in improving the creep resistance of these steels. The low tempering temperature of 963 K (690 °C) is enough for the precipitation of the full volume fraction of both MX and M₂₃C₆. A high boron content, more than 1 at. pct, was found in M₂₃C₆ precipitates and they grow slowly during aging. The high boron level in the steel results in metal borides rather than BN with the approximate formula (Mo_0.66Cr_0.34)₂(Fe_0.75V_0.25)B₂. Two families of MX precipitates were found, one at lath boundaries about 35 nm in size and one dense inside the laths, only 5 to 15 nm in size.